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Hello again,
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The results of today's Ham Flea Market is an
Ameritron AL-811 HF Power Linear Amplifier
for a more than fair price which included two
extra tubes... This unit is the three tube version.
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Dentron, Amp Supply and Ameritron are/were
offered as bargain priced quality amplifiers,
Ameritron still in business and offering a broad
based line up of current models which include
an 811a tubed unit or two.
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I get it home and pop the cover off, much to
my surprise the unit is clean and very operational...
wonders never cease.
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Here are some quick comments as to the
units design and construction.
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In order to reduce production costs, the amplifier
features two main boards, one can be considered
the low level board where the tuned input, relay t/r
circuit, alc, power supply and generic misc functions
live.
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The other high level board contains the power
HV supply and part of the output tank circuit, the
upper frequency coil, some band switching traces
and coupling/bypass capacitors.
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It's my opinion the amplifier is a practical real
world trade off which seems to work out well
for the budget minded amateur.
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Here are some less impressive features which
could stand improvement(s).
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1) Cooling.
There is one mini boxer type fan which is rear
panel placed behind the transformer... quite a
distance from the tubes. Although the chassis
appears to be pressurized to some extent, the
tubes live perpendicular to the vent holes and
provide uneven cooling.
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Operation at higher power levels might not provide
proper cooling to the tube(s) farthest away from the
vent holes. Excessive heat kills electronic
parts quickly...
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The cooling might need to be improved for a
more serious contest operator. I just don't like
the uneven cooling physical layout.
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2) Glitch Diodes
Even though this amplifier is a bargain priced
unit, diodes are cheap insurance for meter
and glitch protection. This units protection
diodes should be upgraded from 1N4007 to
something a little heftier, say a 1N5408.
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Additional diodes should be added in places
well described on Rich's web page.
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3) Part Updates.
The output choke should be replaced with a
resistor. MOV's seem to have missed this
amps power supply....
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I will say that the amplifier appears to operate
well and uses a lot of generic - industry
standard parts.
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The two large pc boards are a bit of a turn off
for me. The upper frequency tank coil is pc board
mounted and the traces are quite long relative to
what they could be. I'd be willing to bet the 10
meter band has reduced output which could be
increased with a better input/output tank circuit
layouts. But where else can you buy an amplifier
of this "class" for a similar price..?
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More to come after I play with it a bit more...
Your results may vary.
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cheers
skipp
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